摘要:

AbstractA new physics approach is presented to evaluate the theoretical transmutation potential of different nuclear power systems (standard or advanced fission reactors and hybrid accelerator/sub-critical blankets). The nuclei to be transmuted are the transuranium (or transplutonium) isotopes produced in the irradiation of naturally occurring fuels (uranium or thorium) and the fission product isotopes. The analysis is based on an evaluation of neutronic constraints on the transmutation rates integrated over the life of the nuclide families, taking into account the overall neutron balance of the system being considered. This method allows a comparison of the potential of different systems and establishes physics limitations, particularly in the field of fission product transmutation.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21476

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractIn view of the importance of so-called“sequential reactions”in fusion reactor structural materials, the production of radioactivity due to sequential reactions associated with protons emitted via (n,xp) reactions with 14.9-MeV neutrons has been measured. The effective production yields with respect to 14.9-MeV incident neutrons produced by sequential reactions were obtained for the radio active products of48V,56Co, and64Zn in titanium, iron, and copper, respectively. The values were 14.7±1.9, 4.6±0.3, and 11.4±1.9μb, respectively. The effective production cross section was estimated on the basis of all relevant data on (n,xp) and (p,n) cross sections, proton emission spectra, and the proton stopping power in these materials. This analysis gave values 22% larger, 29% smaller, and a factor of 5.6 smaller than the measured values for these reactions, respectively. The range of these discrepancies is not unreasonable considering the large uncertainties in the data base used in the estimation.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21477

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe activation cross sections for the99Tc(n,p)99Mo,99Tc(n,α)96Nb,99Tc(n,n′α)95Nb, and“Tc(n,n′)99mTc reactions at 13.5 and 14.8 MeV have been measured by using the deuterium-tritium neutron generator (the Fusion Neutronics Source) at the Japan Atomic Energy Research Institute. The results were compared with experimental values from the literature, evaluated activation cross-section files, and predictions by current cross-section computer codes. Special emphasis was placed on the feasibility of producing high-specific-activity“Mo, to be used in medical applications, via the99Tc(n,p)99Mo reaction in the Fusion Material Irradiation Facility. A factor of 3 overestimate of99Mo production resulted when the REAC *2 code was used. It is suggested that this discrepancy is due primarily to the factor of 5 difference in cross sections at the 14-MeV region between the REAC*2 data and the current measurement.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21478

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractOn the basis of successful studies on the pickup mechanism of composite particle emission and the angular distribution of single-nucleon emissions, a theoretical method for calculating the doubledifferential cross section of alpha-particle emissions is proposed. As an example, the double-differential cross sections of alpha particles in the neutron-induced56Fe(n,xα) reaction have been calculated at En= 14.5 MeV. The theoretical results reproduce the experimental data successfully.

ISSN:0029-5639    

DOI:10.13182/NSE93-28

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractTwo techniques for solving the mathematical adjoint equations of an interface current nodal method are described. These techniques are the“similarity transformation”procedure and a direct solution scheme. A theoretical basis is provided for the similarity transformation procedure originally proposed by Lawrence. It is shown that the matrices associated with the mathematical and physical adjoint equations are similar to each other for the flat transverse leakage approximation but not for the quadratic leakage approximation. It is also shown that a good approximate solution of the mathematical adjoint for the quadratic transverse leakage approximation is obtained by applying the similarity transformation for the flat transverse leakage approximation to the physical adjoint solution. The direct solution scheme, which was developed as an alternative to the similarity transformation procedure, yields the correct mathematical adjoint solution for both flat and quadratic transverse leakage approximations. In this scheme, adjoint nodal equations are cast in a form very similar to that of the forward equations by employing a linear transformation of the adjoint partial currents. This enables the use of the forward solution algorithm with only minor modifications for solving the mathematical adjoint equations. By using the direct solution scheme as a reference method, it is shown that while the results computed with the similarity transformation procedure are approximate, they are sufficiently accurate for calculations of global and local reactivity changes resulting from coolant voiding in a liquid-metal reactor.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21480

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe temporal subdomain method (TSM), based on a spatial finite element formulation, is investigated as a method for the solution of the space-time-dependent multigroup neutron dynamics equations. The spatial aspect of the problem was formulated as an array of finite elements by using a two-dimensional rectangular coordinate system subdivided into contiguous triangular elements. Within each element and within each neutron group, the flux was represented by a linear polynomial. Numerical experiments using a computer program developed during the course of the investigation demonstrated that the method is straightforward to implement and that it produces stable calculations for a wide range of time steps. The stability of the method has been tested for sinusoidal, ramp, and step-change reactivity insertions. The results show that the TSM outperforms most alternating direction implicit methods in the sense that a similar degree of accuracy can be achieved with larger time steps using the same number of nodes. System condition number calculations as a function of node number were also carried out for a series of static eigenvalue calculations to determine the likelihood of error propagation and the difficulty of inverting the global system matrices during the time-dependent calculations.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21481

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractTime-domain noise analysis techniques such as the Rossi-α, the variance-to-mean, and the interval-distribution methods can be used to measure fundamental reactor parameters in a wide variety of reactor systems, provided the power level of the system is not too high. Simple expressions have been derived that define the maximum power level (i.e., the“reactor noise threshold”) above which time-domain reactor noise techniques are likely to fail in subcritical, critical, and supercritical systems.

ISSN:0029-5639    

DOI:10.13182/NSE94-A21482

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor